Circuit interrupting device



' oct. 28, 1941. H, 1 CRABBS 2,261,020

CIRCUIT INTERRUPTING DEVICE Oct. 28, 1941. H. J. cRABBs 2,261,020

CIRCUIT INTERRUPTING `DEVICE Patented er. 2s, 1941 i 2,261,020I CIRCUIT INTERRUPTmG DEvIen Herbert. J. Crabbs, Wiikinsburg, Pa., assigner to West inghouse Electric & Manufacturing Company, lEast Pittsburgh, Pa., a corporation of Pennsylvania Appueaan November 12, 1937, serial No. 174,202

(el. 20o-145) 12 Claims.

The invention relates to electricalcircuit controlling devices in general and more particularly to air break circuit interrupting devices for high voltage circuits.

An object of the invention is the provision of an improved circuit interrupting device for high voltage circuits embodying means for controlling and extinguishing either large or small current arcs.

Another object of the invention is the provision of an improved circuit interrupter for high voltage circuits that.is capable of safely interrupting currents from as low as a fraction of an ampere up to relatively high currents within its short circuit rating.

Another object of the invention is .the provision of van improved circuit interrupting device embodying a plurality of pairs of serially connected separable contacts, an actuating member movable through a relatively short stroke for opening said pairs of contacts in a predetermined order, and arc extinguishing means associated with the contacts for extinguishing arcs of different current magnitude at diiierent points of travel of the actuating member.

Another object of the invention is the provision of an improved circuit interrupting device of the type previously described that is simple and compact in construction, safe and reliable in operation, and inexpensive to manufacture.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will best be understood from the following detailed description of several ernbodiments thereof when read in connection. with the accompanying drawings, in which:

Figure l is a side elevational view, partly in section, of the circuit interrupting device constructed in accordance with the invention;

Fig. 2 is a bottom plan view of the device illustrated in Fig. 1;

Fig. 3 is a view similar to Fig. 1 illustrating the open circuit position of the lnterrupter;

Fig. 4 is a vertical sectional view of a modified form of the circuit interrupting device, illustrating the position of the parts in the closed circuit position of the device:

Fig. 5 is a sectional view similar to Fig. 4 illustrating the position of the parts in the-first portion of an Vopening operation:

Fig. 6 is a seetionai view similar to Figs. 4 and' '29 and 3l.

5 illustrating the position of the parts in the full open circuit position of the device; and

Fig. 7 is an enlarged horizontal sectional view of the devic shown in Fig. 4, the view being taken substantially on the line VlI-VII thereof and looking in the direction of the arrows.

Referring to Figs. 1 to 3 of the drawings, the circuit interrupting device constructed in accordance with the invention comprises in general a plurality of spaced hollow insulating tubes 3, Il and I3, and a plurality of pairs of separable contacts consisting of the stationary contacts I5, I'I' and I9 and the cooperating movable conducting plungers 2l, 23 and 25. The hollow tubes 3, I I and I3 are composed of a suitable brous material, such as hard iibre, which readily decomposes when acted on by an arc to give of! a large quantity of deionizing or arc extinguishing gas which intermingles turbulentlyewith the arc stream to extinguish the same. 'I'he bores of the tubes 3, I I and I3 are all of substantially the same diameter and have a relatively close t with the movable plungers 2l, 23 and 25.. If desired, the tubes may be formed of other suitable insulating material and lined with an arc extinguishing material. connected by a plurality of insulating plates 2l, A bracket 33 has its ends rigidly secured to the plates 29 and 3l, and this bracket is adapted to be secured to any suitable form of support and insulated from ground for line potential. The upper end of the bore of the tube 9 flares outwardly, as indicated at 35, to form an enlarged mouth for the exit of gases formed within the tube 9 during circuit interruption. The tubes II and I3 are of greater length than the tube 9, and the upper ends of these tubes are closed by suitable plugs 31 of insulating material, the plugs being retained in the upper ends of the bores by means of pins 39.

The conducting plungers 2|, 23 and 25 are d1s posed for axial movement in the bores of the tubes 9, II and I3, respectively. and the plungers all have substantially the same diameter or cross section. The diameter of the conducting plungers is slightly less than the diameter of the bore of the tubes by an amount suiiicient to permit free axial movement of the'plungers within the tubes. The lower ends of the conducting plung-44 ers are mechanically connected for movement together by means of a tie plate 4I of insulating material. The lower ends of the plungers are reduced and pass through openings 43 provided therefor in the tie plate 4I. The lower ends of the reduced portions of the nlungers are thread- The tubes are spaced and mechanically ed for receiving the clamping nuts 45, which serve to secure the plungerls tothe tie plate 4I. 'I'he length of the conducting plunger 2l is substantially the same as the length o! its corresponding insulating tube 9, so that the upper end of the plunger lies substantially In the plane of the upper edge of the tube S in the closed circuit position of thedevice. The conducting plungers 23 and 25 are gf greater length than the plunger 2i for a purpose which will be hereinafter d escribed.

The stationary contact I5, which cooperates with the plunger 2|, is secured to the end of a strip Il of resilient conducting material. the cpposite end of which is secured to the odset portion 49 of a bracketSI by means of a bolt 53 and a nut 55. The bolt 53 serves as a terminal bolt for connecting the stationary contact I and the resilient strip 4l to the conductor 51 of an electrical circuit. The bracket 5I is -secured to and supported by the insulating tube 9 in any suitable manner.

The stationary contacts lII and ITS, which cooperate with the conducting plungers 23 and 25,

are mounted within an insulating tubular con-Y tact holder 59, which is threaded at each end into the tubes II and I3. T'hecontacts I1 and I9 are slidably mounted in the contact holder 59, and are biased outwardly of the holder by means of a light coil spring 5I. The spring 5I serves to bias the contact I'I into engagement with the side of the conducting plunger 23, and

the contact I3 into engagement with the side of its cooperating conducting plunger 25. The contacts Il and I9 are electrically connected by means of a exible shunt conductor 63.

The contact holder 6I and the stationary contacts I1 and I9 mounted therein are' disposed substantially intermediate the length of the insulating tubes II and I3, and the lengths of the conducting plungers 23 and 25 are such that a portion of these plungers extends above the contacts Il and I9, so that the contacts I'I and I9 Y remain in engagement with their corresponding conducting plungers 23 and 25 during the first portion of the opening movement ot the plungers after the plunger 2I has separated a predeter- The tie plate AI, which serves to mechanically shown) is mounted a spring-pressed contact 5l (Fig. 2).

The contact 6l is biased inwardly into engagement with the side of the conducting plunger 25 by means of a coil spring 59. 'Ihe terminal bushing 65 is provided with a threaded terminal stud 1I for receiving a terminal nut .13, the stud Il and nut 'I3 forming a second' terminal for connecting the device in an electrical circuit.

The electrical circuit through the interrupter extends' from the right-hand terminal 53 through the resilient strip 4l, stationary contact I5, conducting plunger 2I, through a bridging strip 'I5 of conducting material to the conducting plunger 23, stationary contact Il, flexible shunt 53, stationary contact I5, the conducting plunger 25 to the stationary terminal contact 61 and terminal stud 1I.

The conducting plungers 2|, 23 and 25 'are biased downwardly to open circuit position by means of tension springs SI, the upper ends of which are secured to the eye plates ll.

The conducting plungers are releasably held in closed circuit position, as illustrated in Fig. l, by means of a trip device indicated generally at 83. The tie plate II is provided with a latch piece B5, which is adapted to normally be engaged by a latch member 8l to hold the interrupter in closed circuit position. The latch member 8T is connected for movement with the movable core 89 of the solenoid 9|, and is biased to latching position, as shown in Fig. l, by means of spring 93. bracket 95 which is secured to the insulating plate 2l. The solenoid SI may be made responsive to any one oi' a plurality of abnormal electrical conditions in the circuit to be controlled to trip the interrupter, or its energization may be controlled manually from som'e remote point.

The operation oi the interrupter as thus i'ar described is briefly as follows: Upon energizetion of the trip devicel33, the tie plate II is released, and the biasing spring BI moves the tie plate 4I and all of the conducting plungers 2l,

23 and 25 in a downward direction to open circuit position. The downward movement of the conducting plungers first causes the plunger 2| to separate from its stationary contact I5. During this portion of the downward movement of the plungers, the contacts I'I and I3 still engage the upper vportions of 'the conducting plungers 23 and 25. Continued downward movement of the plungers after the plunger 2i has separated a predetermined distance from its stationary contact I5 causes the conducting plungers 23 and 25 to disengage and separate from the stationary contacts Il and I 9 to introduce additional gaps in the circuit. The full open circuit position of the plungers is illustrated in Fig. 3. l

. Duringthe above-described circuit opening operation, an arc is iirst drawn between the conducting plunger v2| and the stationary contact I5. If this arc is not extinguished in the lnsulatingltube 9 by the time the plungers 23 and 25 begin to separate from their stationary contacts Il and I9, additional arcs are drawn between these plungers and their corresponding stationary contacts.

The bores of the insulating tubes 9, II and I3 form arc chambers or passages for the arcs drawn between the plungers and their corresponding stationary contacts. The dimension of the arc passage formed by the bore ofthe tube 9 is such that arcs of high current magnitude are eilectively extinguished therein before the conducting plungers 23 and 25 separate from their corresponding stationary contacts I1 and I9. This results from the fact that arcs of high current magnitude are of such size as to intimately en- 'I'he solenoid 9i is carried `by a l the tube 9 from becoming large enough to damtlu's tube. If'the arc drawn between the punger 2| and the stationary contact I5 is of lower current magnitude, it may not be extinguished within the tube 9. This is due to the fact that the arcs of lower current magnitude are smaller and may not play upon the inner surface of the tube 9 so as to produce a sufiicient quantity of arc extinguishing gas to extinguish these arcs. In such instance, additional arcs will be drawn between the conducting plungers 23 and 25 and the stationary contacts I1 and I9. When these plungers separate from their contacts, the reduced portions $4 of the followers 62, connected to the upper ends of the conducting plungers 23 and 25, serve to restrict and conne the arcs drawn between the plungers 23 and 25 and the stationary contacts I1 and I9, causing the arcs to intimately engage the inner surface of the tubes and I3, and also the surfaces oi the followers 62. Due to the confinementA of these arcs and the intimate engagement thereof with the material of the tubes and I3 and the followers G2, a suflicient quantity of arc extinguishing gas is liberated to effectively extinguish arcs of a current magnitude within a certain range below high magnitude currents.l If the arcs are of a current magnitude so low that they are not extinguished by the partial coniinement provided by the reduced portions 64 of the followers 62, the continued downward movement of the plungers during the latter part of the' opening operation brings the unreduced upper portions of the followers 62 into engagement with the stationary contacts |1 and I9. The unre- `duced upper portions of the followers serve to further restrict and confine the arc passages and the arcs to produce a sufiicient deionizing action to effectively extinguish these low current arcs. It will thus be seen that arcs of high current magnitude are effectively extinguished in the tube 9 between the plunger 2| and the stationary contact I5, and arcs of lower current magnitude are effectively extinguished within the tubes and I3.

The insulating tubes and I3 are provided with vents I| and |03 to relieve the pressure of the arc gases. it will be noted that vents |0| in the tube direct the arc gases in a diierent direction from the direction given by the vents |03 in the tube i3, while the arc gases developed in the tube e are directed in still another direction. This arrangement of the vents minimizes the possibility of trouble from the arc gases uniting to cause an external nashover.

The plungers 2i and 23 are at the same potential but the plungers 23 and 25 in the open position of the device have a difference of potential between them. In'order to prevent any arc gases that may be forced out of the lower ends of the tubes II and I3 from intermingling and causing an external lashover, a barrier |05 is provided.- The barrier |05 is secured at its lower end to the tie plate 4I for movement therewith, and is of a length such that its upper portion lies between the lower ends of the tubes and I3 in the open circuit position of the device.

Ii desired, the interrupting device previously described may be used inconnection with a dis.

connect or air break switch, so as to interrupt the circuit and extinguish the arc before the switch blade opens. 1n such instance, the interrupting device may be associated with the switch in substantially the same manner as the interrupting device disclosed in the copending application of S. T. Schofield and J. H. Frakes, Serial No. 126,890, filed February 20, 1937, and assigned to the assignee of this invention, now Patent 2,172,225, issued September 5, 1939. In such combination, the trip device 83 would, of course, be omitted and the interrupter biased to closed circuit position and provided with a hook to be engaged by the actuator carried by the switch blade as in the case of the interrupter disclosed in the aforementioned copending application of S. 'I'. Schofield, et al.

A modified form of the circuit interrupter is illustrated in Figs. 4 through 7 of the drawings. In this modification of the invention, the stationary contacts and movable conducting members are carried by and disposed in a single insulating tube, thus eliminating the danger of adjacent arcs causing an external flashover. Referring to Figs. 4 through 7 of the drawings, the circuit interrupter illustrated comprises in general a hollow insulating tube |01, a plurality of stationary contacts |09, and H3, and a cir- V cuit controlling plunger or member ||5, which has a plurality of contact members or conductwith the stationary contacts |09, III and ||3` to form a plurality of pairs of separable contacts.

The hollow insulating tube |01 is composed of a iibrous insulating material, such as hard fibre, which, when acted on by an arc, gives off large quantities of deionizing or arc extinguishing gases to extinguish the arc. If desired, the insulating tube |01 may be composed of other. insulating materials and lined with a material which gives off an arc extinguishing gas. The tube |01 is enclosed and protected by an outer insulating tube |23 which is secured to the inner tube |01 in any suitable manner.

The circuit controlling plunger or member ||5 is disposed for axial movement within the bore of the tube |01, and its diameter is slightly less than that of the bore so s to permit free axial movement thereof within the bore. The conducting sections ||1, ||9 and |2| are insulated from one another by the sections or followers |25, which are composed of a suitable insulating material similar to the material of the tube |01. The insulating followers |25 are threadedly connected at each end to the conducting sections or contact members I1, l I9 and lidi.

The, stationary Vcontact Ig, which cooperates with the contact member Ill, is carried by one end of a strip i2`| of resilient conducting material, the opposite end of which is secured to a bracket I2?) by means of a terminal bolt ISI and nut |33. The terminal bolt Ii forms one terminal of the interrupter and serves to connect the interrupter to a conductor |35 of an external circuit.

The upper end of the bore of the tube |01 is flared outwardly, as indicated at I3|,`to provide an enlarged mouth adjacent the stationary contact |09 for the exit of gases produced by the arc between the contact member ||1 andthe stationary contact |09.

The stationary contacts and H3, which cooperate with the contact members ||9 and |2|,

||9 and |2| engage their corresponding station-v ary contacts |09, III and ||3 in the closed circuit position of the interrupter, as is illustrated in Fig. 4. The stationary contacts II I and II3 are so disposed in the tube |01 that in the closed circuit position of the interrupter they engage their corresponding contact members IIS and I2I a predetermined distance below the upper ends of these contact members, so that during opening movement of the member I I5, the contact member ||1 first separates from its stationary contact |09, during which time the stationary contacts I I I and I I3 still remain in engagement with their c .responding contact members IIS and 62|, respectively. At a later point in the opening movement of the member I|5, the contact members IIS and |2| separate from their corresponding stationary contacts |I| and |I3.

The plurality of pairs of separable contacts formed by the stationary c'ontacts I 09, .III and H3 and the movable contact members |I1, IIS and |2I are connected in series circuit relationship by means of the contacts |4| and |43 and the bridging contact strips |45 and I41, The

' stationary contacts NI and |43 are mounted in suitable transverse openings provided therefor in the insulating tube |81, and are biased to engage the contact members||1 and H9, respectively, by means of the springs I 48. The contact I4I is so disposed that it engages the contact member @i1 throughout its range of movement from .closed to open circuit position, and likewise the Contact I 43 is so disposed as to engage the contact member IIS throughout its range of movement from closed to open circuit position. The contact I4! is electrically connected to the stationary contact III by means of the conducting strip |45, andthe stationary contact |43 is electrically connected to the stationary contact I I3 by the conducting strip |41. The movable contact members IIT, IIS and I2I all have substantially the same cross sectional area.

An operating eye |I is threaded on the lower end of the lowermost contact member I2I, and this eye is provided with a terminal means |53 which forms the opposite'terminal of the interrupter. The circuit controlling member II5 is biased downwardly to open circuit position by means of a tension spring |55 which is connected at its upper end to the operating eye I 5|.

The circuit controlling member II5 is adapted to be releasably held in closed circuit position, as shown in Fig. 4, by means of an electro-responsive trip device indicated generally at I 51. The trip device comprises a latch piece |59 carried by the operating eye I5I and a latch member iSI for normally engaging the latch piece. The latch member ISI is connected to the movable core |63 of a trip solenoid |65 and is biased to latching position by means of a springr |61. The

the operating eye |5I is released and the circuit controlling member IIS is moved downwardly to open circuit position by means of the spring |55. During the rst part of the opening movement of the member II5, the contact member II1 separates from its stationary contact |09. During this portion of the opening movement, the contacts I II and I I3 remain in engagement with the upper portions of their corresponding contact members II 9 and |2I. At a later point in the opening movement of the member |I5, contact members IIS and I2| separate from their corlatch controlling solenoid |65 may be maded responsive to any abnormal circuit conditionrso as 'to trip the interrupter in response to predetermined conditions.-

The operating eye I5I. is adapted to be connected to a suitable operating member for closing responding stationary contacts III and II3 to introduce additional gaps in the circuit, as shown in Fig. 5. The nal full open circuit position of the circuit controlling member II5 is illustrated in Fig. 6. y

,During the opening movement of the circuit controlling member IIS, an arc is first drawn between the contact member I I1 and its'stationary contact |09. If this arc is not extinguished before the contact members |I9 and I2I separate from tlieir stationary contacts II I and` I I3, additional arcs in series are drawn between the contact members IIS and I2| and their stationary contacts III and IIS during the latter part of the opening movement when these Contact members separate from their stationary contacts.

The arc extinguishing operations of this modification of the circuit interrupter are substantially identical to the arc extinguishing operations of the originally described embodiment. Arcs of high current magnitude are effectively extinguished between the contact member II1 and the stationary contact |09 in the first part of the opening movement of the circuit controlling member prior to separation of the Contact members II9 and |2I from their stationary contacts III and |I3. Arcs of lower current magnitude drawn between the contact members I I9 and |2I and their corresponding stationary contacts are extinguished during the latter part of the opening operation. This results from the fact that the followers |25, which are provided with reduced portions |69, provide restricted arc passages for the arcs drawn between the contact members IIS and I2| and their corresponding stationary contacts.

The insulating tube IU1 and the outer tube are provided with suitable ventsv I1I adjacent the contacts III and II3 to provide an exit for the gases formed during arcing.

In both of the embodiments of the invention previously described, it will be noted that the actuating member moves through a relatively short stroke from closed to open circuit position to eiectv the separation of the plurality of pairs of contacts in a predetermined order, and arcs of high current magnitude are extinguished duringthe initial portion of the opening movement, while arcs of lower current magnitude are extinguished during a later part of the opening movement. With the proper selection of stroke and dimensions of the arc passages, the interrupter will control and interrupt currents from a fraction of an ampere up to the short circuit interrupting ability of the device. The number of pairs of separable contacts may be increased or decreased to' suit the particular requirements of the device.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. It is desired, therefore, that the language of the appended claims be given the broadest reasonable construction permissible in view of the prior art.

I claim as my invention:

l. In a circuit interrupting device, a plurality of pairs of separable contacts connected in series in the circuit to be interrupted, means including an actuating member movable through a relatively short stroke for first opening one of said pairs of contacts and thereafter opening the remaining pairs of contacts, means forming arcing passages adjacent each pair of contacts, the inner surface of the passages being of a material which gives off a large quantity of gas when acted on by an arc, the construction and dimension of the arc passage for the pair of contacts which are rst opened being such'as to extinguish high current arcs between said pair of contacts to finally interrupt the circuit upon short circuit or heavy overload, and the construction and dimension of the passages adjacent the remaining pairs of contacts being such as to extinguish lower current arcs. A

2. In a circuit interrupter, a plurality of pairs of separable contacts connected in series in the circuit .to be interrupted, means including an` actuating member operable to rst separate one of said pairs of contacts and thereafter separate the remaining pairs of contacts, means enclosing the paths of movement of rsaid contacts having its inner portion`of a material which gives off a deionizing gas when acted on by an arc, the enclosing means adjacent the pair of contacts which are first separated serving to extinguish arcs above a predetermined current magnitude to finally interrupt the circuit upon short circuit or heavy overload, means restricting the arcs of lower current magnitude drawn between the remaining pairs of contacts and causing said arcs to intimately engage the inner portion of the enclosing means to effect extlnguishment thereof.

3. In a circuit interrupter, a plurality oi' pairs of separable contacts connected in series in the circuit,`means including an actuating member operable to rst separate one oi said pairs of contacts and thereafter separate the remaining pairs of contacts, means enclosing the path oi movement of said. movable contacts, the inner portion or said means being oi material which gives off a deionizing gas when acted on. by arc. the enclosing means adjacent the ci contacts which are lrst separated serving to extinguish arcs in excess oi" a predeterufiined. current magnitude to :finally interrupt the circuit uponshort circuit or h eavy overload, and insulating followers movable with the movable contacts of the remaining pairs of contacts, said followers restricting the arcsof lower current magnitude and forcing the arcs into intimate contact with the inner portion of the enclosing means to effect extinguishment thereof.

4. In a circuit interrupter, a plurality of hollow tubes the inner portions of which are of a material which gives off a deionizing gas when acted on by an arc, a conducting plunger movable in each tube, means for simultaneously moving all of said plungers to open and to closed circuit position` a plurality of stationary contacts one for each plunger disposed so that during a circuit opening operation one of said plungers tlrst disengages its stationary contact and thereafter the remaining plunger disengages its stationary contact, an insulating follower movable with said remaining plunger to restrict the arc 4drawn thereby, and means connecting said contacts and plungers in series in the circuit.

5. In a circuit interrupter, a single hollow tubular member, the inner portion of which is of a material which gives ol a deionizing gas when acted on by an arc, a circuit controlling member movable in said tubular member to open and to closed circuit position, said member having aplurality of conducting sections separated and insulated from one another by insulating sections, a plurality of stationary contacts, at least one for each conducting section, engaged by said conducting sections in the closed position of the circuit controlling member, said contacts being disposed so that during a circuit opening operation one of said conducting sections ilrst separates from its stationary contact and at later points the remaining conducting sections separate from their corresponding contacts.

6. In a circuit interrupter, a plurality of hollow tubes the inner portions of which are of a material which gives off a deionizlng gas when acted on by an arc, a conducting plunger movable in each tube, means for simultaneously moving all of said plungers to open and to closed circuit position, a plurality of stationary contacts one for each plunger disposed so that during a circuit opening operation one of said plungers first disengages its stationary contact and thereafter the remaining plungers disengage their stationary contacts, insulating followers movable with said remaining plungers to restrict the arcs drawn thereby, and means connecting said contacts and plungers in series in the circuit, said tubes being vented in different directions for exit of the arc gases.

'7. In a circuit interrupting device, means forming a plurality of conning arc chambers of substantially the same cross sectional area, means comprising a plurality of movable contact members one in each chamber electrically connected in series in the circuit and operable to first draw an arc in one of said chambers and then draw an arc in the other of said chambers if the arc in said first chamber has not been extinguished, said contact members al1 having substantially the same cross sectional area, and means for restricting the arc drawn in the aforementioned other chamber to cause interruption of low current arcs therein.

8. a circuit interrupter, means forming a plurality of ccmining arc chambers all substanun tialiy of the same cross section, a stationary conf" 'tact and a cooperating movable Contact member for each chamber, said contact members being electrically connected in series in the circuit and all having substantially the same cross sectional area, an actuating member movable to first cause separation of one of said movable contact members from its stationary contact and for thereafter causing separation of the other movable contact member from its stationary contact, and a follower connected to said other movable contact member for restricting the arc drawn thereby.

9. In a device for interrupting an electrical circuit, means forming a plurality of conning arc passages, the ilrst of said passages being relatively wide for extinguishing high current arcs to finally interrupt the circuit when the magnitude of the current is large, and the other of said passages being relatively narrow for extinguishing lower current arcs, and means connected in series in the circuit to be interrupted for irst drawing an arc in said nrst passage and for then drawing arcs in the other passage if the arc continues in said first passage.

10. in a device for interrupting an electrical circuit, means forming a plurality of arc passages of diiierent arc extinguishing ability, said passages having the interior thereof of a solid material which when acted on by an arc gives oi a volume of arc extinguishing gas, means electrically connected in series in the circuit to be interrupted for causing arcs in said passages, one of said passages being of relatively large cross section for interrupting large current arcs to finally interrupt the circuit when the magnitude of the current is large, and the other passage being of relatively small cross section to interrupt arcs of lower current magnitude.

11. In a device for interrupting an electrical circuit, a plurality of pairs of separable contacts connected in series in the circuit to be interrupted, an actuating member movable through a relatively short stroke for iirst opening one pair of said contacts and for thereafter opening the remaining pairs of said contacts, means associated with said contacts forming a plurality of arc passages one for each pair of contacts,

the passage for the pair of contacts which are first opened being of relatively large cross section for interrupting large current arcs to finally interrupt the circuit when the magnitude of the current is large, and the other passages being of relatively small cross section to interrupt arcs of lower current magnitude.

12. In a circuit interrupter, a plurality of pairs of separable contacts connected in series in the circuit to be interrupted, means including an actuating member operable through a relatively short stroke for iirst opening4 one pair of said contacts and for thereafter opening the other pairs of said contacts, an'arc extinguishing structure associated with said contacts forming a relatively wide arc passage for said pair of contacts which are iirst opened for extinguishing large current arcs to finally interrupt the circuit when the magnitude of the current is large, and forming narrow arc passages at said other pairs of contacts for extinguishing lower current arcs.

HERBERT J. CRABBS. 

